Re: repro Bendix-style brake booster issue
[Re: 68red440]
#1603329
04/05/14 03:24 PM
04/05/14 03:24 PM
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Joined: Dec 2003
Posts: 329 Cincinnati, OH
68red440
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enthusiast
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OP
enthusiast
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Posts: 329
Cincinnati, OH
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Holy crap these brakes grab hard! Apparently the brake assist was helping so much with the pedal feel that I thought I had no brakes when idling in park. With the rear wheels off the ground I ran it through the gears and found the brakes actually were working. I drove it around the neighborhood and it feels like it has hydroboost! Time for some road tests!
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Re: repro Bendix-style brake booster issue
[Re: 6PakBee]
#1603331
04/05/14 07:11 PM
04/05/14 07:11 PM
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Joined: Dec 2007
Posts: 18,157 Mass
DAYCLONA
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Quote:
Quote:
.....Yes, I believe air is being sucked into the booster when I turn the engine off. Since air should not pass through the back of the booster, the booster is probably bad. Not sure how or why at this point.
The air inlet into the booster is at the rear of the booster around the pushrod. When you press the brake pedal air is admitted into the rear half of the booster. But it shouldn't be leaking when the brakes are released. Just a question, are you sure the booster pushrod is fully extended with the pedal at rest? You see what I'm getting at?
I hope the OP adjusted the booster to master cylinder clearance gap (generally no more than .060 max) before installing his master?
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Re: repro Bendix-style brake booster issue - <resolved>
[Re: 68red440]
#1603333
04/06/14 01:56 AM
04/06/14 01:56 AM
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Joined: Dec 2007
Posts: 18,157 Mass
DAYCLONA
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I Live Here
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Quote:
Before installing, I measured a gap of ~.030. I drove it a lot today, and am really happy with it. It's working way better than I expected! The pedal feel is so different from what I was used to. So I assumed there was something wrong, but there wasn't. Huge relief.
Thanks for the input.
I usually run the dual diaphram Bendix booster on my Mopars, along with 4 wheel discs....pedal feel is drastically different than the single diaphram Midland/Chrysler boosters...my pedal travel with the dual diaphram Bendix and 4 wheel discs is approx 1/2" when the pads are fresh, and 3/4" when the pads are about 1/2 worn, but the pedal/power assist is impressive with the Bendix, but it is a vacuum hog!
Glad your system is A-OK!
Mike
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Re: repro Bendix-style brake booster issue - <resolved>
[Re: 6PakBee]
#1603335
04/06/14 03:02 PM
04/06/14 03:02 PM
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Joined: Dec 2003
Posts: 329 Cincinnati, OH
68red440
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enthusiast
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OP
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Posts: 329
Cincinnati, OH
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You're absolutely right 6PakBee. Even though the brakes work great, the hissing of air into the back of the booster needs to be corrected. It's acting like a small, controlled vacuum leak on the engine.
The push rod gap was .030 prior to installation, but the gap AFTER installation is what matters. When I push the pedal in ~1/8", the hissing goes away which tells me my pushrod gap is too large.
When installing the booster with the 4 nuts on the cabin side, I partially compressed the new white foam gasket. I was careful not to over tighten the nuts, but maybe they need to be a little tighter. That would draw the booster back to the firewall. If I draw the booster back another 1/16" (compressing the gasket a little more), it should close the pushrod gap by the same amount. A 1/16" at the linkage would translate to more than 1/8" at the pedal.
When it stops hissing I'll consider it good. The pedal feel and travel is good as it is, but if the brakes start actuating a little higher in the pedal travel that'd be even better. If tightening the nuts isn't enough, I'll pull the master and adjust the rod. I'll let you know what happens.
Seriously, these brakes feel like hydroboost. They're really sensitive like the new Darts that I've test driven recently.
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Re: repro Bendix-style brake booster issue - <resolved>
[Re: 68red440]
#1603337
04/06/14 04:22 PM
04/06/14 04:22 PM
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Joined: Dec 2007
Posts: 18,157 Mass
DAYCLONA
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Quote:
Correction: Compressing the gasket doesn't affect push rod gap. If anything, it moves the pedal a small amount. The gasket did compress from all the activity, so the nuts needed snugging up anyway. I need to pull the MC from the booster and extend the push rod to close the gap to ~.020. However, the instructions clearly say not to remove the MC from the booster because it can ruin a seal inside. I'll ask The Ram Man about how to do it without potentially voiding the warranty. As long as vacuum isn't applied to the booster with the MC off, it should be OK. Thanks for your help.
Horse puckey just remove the master, no need to remove the lines, leave the cover on, the pushrod will/should have a threaded snout, you need to grip the main rod sticking out, and turn the threaded insert in/out for the desired gap, use a set of dial calipers,to measure the depth of the master's bore, and then measure how much rod sticks out from the boosters/master's mounting face and adjust appropriately
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